Nine murine monoclonal antibodies with specificity for human non-small cell bronchogenic carcinomas, as determined by screening against human tumor cell lines and by immunohistochemistry on pathology slides of human tumors, have been developed. These antibodies react with squamous cell lung carcinomas and with some bronchogenic adenocarcinomas, but do not react with adjacent normal lung in immunoperoxidase studies of fixed human tissues. One antibody, 353H10, has been shown to precipitate a protein of 143,000 daltons from cell lysates and cell membranes of positively reacting cells and nothing from cells which do not react by radioimmunoassay. Preliminary data indicates a lethal effect on cells bearing the 143,000 dalton antigen when incubated in vitro with 353H10 conjugated to the A-chain of abrin. A nude mouse model system with animals bearing human squamous cell carcinomas has been developed to test the efficacy of the 353H10/abrin conjugate in vivo. Further characterization of the antibodies against a panel of normal tissues is also now in progress.